|Rank|Nation|Gold|Silver|Bronze|Total|
|---|---|---|---|---|---|
|1|Nigeria|13|5|6|24|
|2|South Africa|11|11|8|30|
|3|Ethiopia|6|3|2|11|
|4|Kenya|5|4|8|17|
|5|Tunisia|2|2|1|5|
|6|Senegal|2|1|3|6|
|7|Ghana|2|0|4|6|
|8|Cameroon|1|4|1|6|
|9|Egypt|1|1|2|4|
|10|Mauritius|1|0|1|2|
|11|Mozambique|1|0|0|1|
|12|Algeria|0|8|1|9|
|13|Madagascar|0|2|1|3|
|14|Zimbabwe|0|1|1|2|
|15|Tanzania|0|1|0|1|
|15|Togo|0|1|0|1|
|15|Burkina Faso|0|1|0|1|
|18|Central African Republic|0|0|1|1|
|18|Uganda|0|0|1|1|
|18|Namibia|0|0|1|1|
|18|Ivory Coast|0|0|1|1|

Question: what is the difference of silver medals between south africa and kenya?
Answer: 7